1. Field of the Invention
This invention relates to the production of electrolyzed water having cleansing and sterilizing effects.
2. Description of the Prior Art
Attention has recently been drawn to electrolyzed water as cleansing water. For example, the production apparatus according to Japanese Patent Application Laid-Open No. 317414/2000 is such that a cathode plate having a large number of openings and an anode plate having no opening face each other, and water is caused to flow along the two electrode plates. As a result, there is produced electrolyzed water having a cleansing effect.
On the other hand, the apparatus according to Japanese Patent Application Laid-Open No. 277385/1994 is such that the anode and cathode form therebetween a long labyrinthine flow passage along which water is caused to flow. As a result, there is produced electrolyzed water having a sterilizing effect, as ozone is generated when electrolyzed water is produced.
According to these prior arts, however, it is difficult to raise the concentration of ozone, since ozone is generated only accidentally.
It is, therefore, an object of this invention to provide a method of producing electrolyzed water having a cleansing effect and a high ozone concentration.
The object is attained by a method in which an apparatus for producing electrolyzed water from a liquid is used for producing electrolyzed water containing ozone, the apparatus having a flow passage formed between and along two plate electrodes located close to each other, a D.C. (direct current) power source for applying a D.C. voltage between the two plate electrodes and a control circuit for changing the polarity of the plate electrodes alternately, the intervals of time T for changing their polarity being set within the range of time as defined by a formula (10) below:
0.5 (sec)xe2x89xa6Txe2x89xa6(1/3)xc3x97(L/V)xe2x80x83xe2x80x83(10) 
where V: the velocity (cm/sec) of flow of a liquid in the flow passage;
L: the length (cm) of the plate electrodes in the direction of flow of the liquid.
A preferred embodiment of apparatus used for carrying out this invention is an apparatus for producing electrolyzed water from a liquid, which has an electrolytic cell, an inlet means for allowing a liquid forced into the electrolytic cell to flow through, a first electrode plate placed in the electrolytic cell, a second electrode plate placed in the electrolytic cell and facing the first electrode plate, a D.C. power source for applying a D.C. voltage to the first and second electrode plates so as to produce a potential difference therebetween, a control circuit for changing the polarity of the plate electrodes alternately, and an outlet pipe through which electrolyzed water produced in the electrolytic cell is let out of the cell. This apparatus is characterized in that the first electrode plate close to the second electrode plate allows a flow passage to be formed between and along the electrode plates, and that the intervals of time T for changing their polarity can be set between 0.5 and 60 seconds.
For the purpose of this invention, the xe2x80x9cplate electrodexe2x80x9d means not only a non-perforated (non-apertured) electrode plate not having any through opening allowing a liquid to flow therethrough, or a perforated (apertured) electrode plate having a large number of (for example, 10 or more) through openings allowing a liquid to flow therethrough, but also a metal net, or the like.
It is said that water molecules form a cluster (aggregation of molecules formed by aggregating molecules) by hydrogen bonding which behaves like a macromolecule. The electrolysis of water, however, forms oxygen gas, hydrogen gas and new water molecules as a result of chemical reactions shown by formulas (1) to (3) below.
H2Oxe2x86x92H++OHxe2x88x92xe2x80x83xe2x80x83(1) 
2H++2exe2x88x92xe2x86x92H2xe2x80x83xe2x80x83(2) 
4OHxe2x88x92xe2x86x924exe2x88x92+O2+2H2Oxe2x80x83xe2x80x83(3) 
These chemical changes destroy the clusters. As a result, water decreases its surface tension and increases its surface activity and thereby its diffusion through contaminant substances. Electrolyzed water contains a large number of fine bubbles, as of hydrogen and oxygen gases, etc. and owing to cavitation (an infinite number of fine and nearly vacuum cavities formed about the bubbles and producing an impact force when they are broken), the water facilitates the separation of contaminant substances from the material to be washed.
It has been confirmed that the electrolysis of city water lowers its surface tension from 0.0722 N/m to about 0.0716 N/m.
According to this invention, water or an aqueous solution is used as raw water (liquid). As raw water is required to be electrically conductive and contain ions in order to realize the chemical reactions according to formulas (1) to (3), city or well water is usually used as xe2x80x9cwaterxe2x80x9d, though pure (or distilled) water or ion exchange water can also be used. An aqueous solution may contain salt, or citric acid.
The amount of water which can be electrolyzed is proportional to the amount of an electric current flowing to the electrodes. It is, therefore, necessary to raise the amount of the current as far as possible to perform electrolysis powerfully. According to this invention, the electrodes have a reduced distance therebetween to receive an increased current without relying upon the application of a very high voltage. The distance between the electrodes is usually required not to exceed 3.0 mm and is preferably from about 0.5 to 2.0 mm. In this connection, it is desirable to employ a plurality of electrode units to obtain a large total electrode surface area.
The first electrode plate and second electrode plate are so disposed as to extend substantially in parallel to each other and face each other to thereby have a substantially uniform distance therebetween, so that the surface of each electrode plates may contribute to electrolysis uniformly.
The xe2x80x9cfacingxe2x80x9d each other of the electrode plates means that there is no diaphragm therebetween.
The reduced distance between the electrodes makes it difficult for water to flow into the space therebetween. According to this invention, therefore, one of the electrode plates has a multiplicity of through holes which make it easy for water to flow into the passage between the electrodes. Moreover, deflecting means is provided for directing raw water toward the holes of the perforated electrode plate so that it may flow into the passage between the electrodes. The deflecting means is preferably defined by a multiplicity of nozzles formed in the inlet pipe.
Water entering the flow passage between the two electrode plates flows therethrough with bubbles and flows out through other holes and the top clearance between the two electrode plates. Therefore, the two electrode plates are preferably disposed not horizontally, but along a vertical or inclined plane to facilitate the flow of the water containing bubbles therebetween.
The electrolysis of water produces fine bubbles of hydrogen and oxygen gases. These bubbles serve as nuclei for an infinite number of fine and nearly vacuum cavities which produce an impact force when they are broken. This phenomenon is called cavitation, and the energy which is produced when the bubbles are broken exhibits an effective washing action.
It is sufficient for water to have an ozone concentration of about 1 mg per liter for sterilization. It is generally said that Escherichia coli, virus or spore bearing bacterium are 99% inactivated in about a minute in water having an ozone concentration of 0.01 mg, 1 mg or 2 mg, respectively per liter. At such a level of concentration in water, ozone has only a very low oxidizing power and does not present any problem of rusting the apparatus for producing electrolyzed water, piping, etc.
It is presumed that if water is electrolyzed by using a non-perforated electrode plate and a perforated electrode plate and reversing the polarity of the electrode plates, the generation of ozone gas is facilitated by the phenomena which will now be described.
If the potential of the non-perforated electrode plate is raised, OH (hydroxyl) radicals are formed on the surface of the electrode plate to produce oxygen atoms, and the combination of such oxygen atoms forms oxygen molecules, as a result of the chemical reactions represented by formulas (4) and (5) below:
OH+OHxe2x86x92O+H2Oxe2x80x83xe2x80x83(4) 
O+Oxe2x86x92O2xe2x80x83xe2x80x83(5) 
In other words, an oxygen molecule (oxygen gas) is produced as shown by the chemical reaction formula (3) before. The oxygen molecules produced on the surface of the non-perforated electrode plate flow toward the through openings of the perforated electrode plate to leave the narrow flow passage between the electrodes with water, and show a high concentration in the vicinity of the openings of the perforated electrode plate.
If under these circumstances, the potentials of the electrode plates are reversed (alternated) so that the potential of the perforated electrode plate may be raised, OH radicals are formed on the perforated electrode plate to produce oxygen atoms. Oxygen molecules are produced on the perforated electrode plate in accordance with the chemical reaction formula (5), and show a still higher concentration in the vicinity of its through openings, since oxygen molecules are already concentrated there as stated above. It is, therefore, presumed that it may be easier for oxygen atoms to combine directly with oxygen molecules, thereby the probability of the generation of ozone may be higher, as shown by formula (6) below:
O+O2xe2x86x92O3xe2x80x83xe2x80x83(6) 
It is, thus, considered that a high concentration of ozone (O3) can be obtained if the polarity of the non-perforated electrode plate and that of the perforated one are changed and alternated at appropriate intervals of time.
The production method of this invention electrolyzes water powerfully, and thereby destroys clusters of water to lower its surface tension and raise its surface activity. Moreover, the method of this invention produces electrolyzed water which is rich in fine bubbles of hydrogen and oxygen gases, etc., and which is excellent as cleansing water owing to not only its surface activity, but also its cavitation effect, even if no detergent may be used.
According to this invention, it is possible to produce electrolyzed water having not only a cleansing power, but also a sterilizing power, since its ozone concentration can be raised by changing the voltages applied to the electrodes at appropriate intervals of time.
As regards the pH (hydrogen ion exponent) of the electrolyzed water which is produced, it maintains the neutral level of the original water. It does not have any chemical substance added thereto, but is environment-friendly.
Moreover, the electrolyzed water produced by the method of this invention has an oxidation-reduction potential which is sufficiently lower than xe2x88x92100 mV to enable the rust-proofing of the cleansing apparatus and its piping.
Tap water generally contains chlorine ions at a concentration of about 10 to 20 mg per liter. If such tap water is electrolyzed, chlorine ions release electrons to the electrode plate and produce chlorine gas in water, as a result of the chemical reaction represented by a formula (11) below:
2Clxe2x88x92xe2x86x922e+Cl2xe2x80x83xe2x80x83(11) 
The chlorine gas produced in water reacts easily with hydroxide ions in water and forms a chlorine ion and residual chlorine ClOxe2x88x92 as a result of the chemical reaction represented by a formula (12) below:
Cl2+2OHxe2x88x92xe2x86x92Clxe2x88x92+ClOxe2x88x92+H2Oxe2x80x83xe2x80x83(12) 
The residual chlorine ClOxe2x88x92 is not a very strong oxidizing agent, but is a substance having a bleaching action and a sterilizing action.
Ozone has a strong sterilizing power immediately after its formation, but is said to have a life of only several seconds to several tens of minutes in water. On the other hand, residual chlorine maintains its sterilizing effect for a long time, though its sterilizing power may be low.
If tap water containing chlorine ions is electrolyzed by the apparatus as described above, it is possible to produce ozone and residual chlorine together, as stated above. Thus, there is produced electrolyzed water having a strong sterilizing power owing to ozone immediately after the electrolysis of tap water and maintaining a certain level of sterilizing power owing to residual chlorine even after the passage of a long time.
An assay for its sterilizing effects on various kinds of bacteria confirmed the effectiveness of water not only immediately after its electrolysis, but also after 24 hours of storage.
Instead of alternating the potentials of the electrode plates as stated above, there is no necessity of alternating the potentials of the electrode plates if the electrode plates vary in form from non-perforated to perforated and from perforated to non-perforated along the flow passage of water.
Thus, another preferred embodiment of apparatus used for carrying out this invention is an apparatus for producing electrolyzed water from a liquid, which has an electrolytic cell, an inlet means for allowing a liquid forced into the electrolytic cell to flow through, a first electrode plate placed in the electrolytic cell, a second electrode plate placed in the electrolytic cell and facing the first electrode plate, a D.C. power source for applying a D.C. voltage to the first and second electrode plates so as to produce a potential difference therebetween, and an outlet pipe through which electrolyzed water produced in the electrolytic cell is let out of the cell. This apparatus is characterized in that the first electrode plate close to the second electrode plate allows a flow passage to be formed between and along the electrode plates, and that each of the two plate electrodes has non-perforated and perforated portions formed alternately and in such a way that each non-perforated portion of one electrode faces a perforated portion of the other.
It is considered that a small amount of ozone is generated even by electrolyzing water without changing the potential applied between the electrode plates, as stated before in connection with the prior art. In that case, however, the gradual deposition of scales of hydroxides composed of calcium, magnesium, etc. on the cathode plate gradually makes the flow of an electric current difficult and brings about a lowering in the efficiency of electrolysis resulting eventually in the generation of hardly any ozone.
Because their polarity is changed before any scale is deposited on the electrodes, if the time to wait for each change of polarity is shorter than a certain level, it is presumed that the generation of ozone is facilitated to some extent even without any through opening, that is, by applying a DC voltage to two non-perforated electrode plates and alternating their polarity. It is also presumed that the generation of ozone is likewise facilitated by applying a D.C. voltage to two perforated electrode plates in an alternating way.